It has conventionally been a general practice to amplify a signal by feeding the signal to an amplifier. It is ideal that the amplifier is a linear circuit. However, it is difficult to manufacture an amplifier which is a completely linear circuit, and an amplifier is thus treated as a type of a non-linear circuit. Namely, if a signal is fed to an amplifier, a distortion component in addition to an amplified signal is output.
A measurement of such a distortion component has been practiced as described in Patent Document 1 (Japanese Laid-Open Patent Publication (Kokai) No. 2001-285211 (ABSTRACT)), for example.
However, a measurement of a phase of a distortion component output from an amplifier has not been practiced conventionally upon a signal having at least two frequency components being fed to the amplifier.
An object of the present invention is to measure a phase of a distortion of a signal output from a circuit to be measured upon a signal having at least two frequency components is fed to the circuit to be measured.